1. Technical Field
The present invention relates to a method of mounting columns onto a ceramic column grid array substrate and also pertains to a column suction-holding head for use in the column mounting method.
2. Description of the Related Art
With the progress of technology to increase the communication speed of electronic devices and to integrate electronic components, there has been a tendency to fabricate multi-function electronic components with an increased number of leads (lead count). Examples of conventional electronic components with increased lead count include QFP, SOIC, etc. There has recently been a demand for electronic components with a further increased number of functions. Conventional multi-function electronic components are short of the number of leads needed to meet the demand. Under these circumstances, use has been made of ball grid arrays (hereinafter referred to as “BGA”), e.g. PBGA, CBGA, and TBGA, as electronic components with further increased lead count. However, BGA suffers from the disadvantage that the BGA substrate may be distorted by heat generated during the use of an electronic device incorporating the BGA substrate. In view of the problem of BGA substrate distortion, a type of grid array having columns in place of solder balls are used as connecting terminals, thereby further improving the ability to absorb thermal stress between substrates. This type of grid array is known as “ceramic column grid array” (hereinafter abbreviated as “CGA”). In CGA, a multiplicity of circular cylindrical columns are installed on a ceramic substrate to make an electric connection between the ceramic substrate and a printed substrate through the columns.
Columns used in CGA are high-temperature solder wires consisting essentially of lead, metal wires, solder-plated metal wires, etc. Various kinds of columns are used according to the size of CGA and the lead count thereof. Generally used columns have a diameter of 0.51 mm and a length of 2.54 mm. In CGA, columns are mounted on a ceramic substrate at right angles to the substrate surface because the ceramic substrate and the associated printed substrate have to be connected to each other accurately through the columns.
When columns are to be mounted on a ceramic substrate, a solder paste is applied to electrodes of the ceramic substrate, and the columns are placed on the solder paste coated portions of the ceramic substrate at right angles to the substrate surface. Thereafter, the solder paste is melted in a heating device such as a reflow furnace, thereby soldering the columns to the ceramic substrate. To mount the columns on the ceramic substrate perpendicularly to the substrate surface, a mounting jig is placed over the ceramic substrate, and the columns are inserted into respective holes of the jig. Thereafter, the ceramic substrate and the jig are heated in a reflow furnace. When a CGA loaded with columns is to be mounted on a printed substrate also, a solder paste is applied to the printed substrate, and the columns of the CGA are placed on the solder paste coated portions of the printed substrate. Thereafter, the solder paste is melted in a reflow furnace to solder the columns to the printed substrate.
In BGA, when solder balls are to be mounted on a BGA substrate, they can be mounted collectively onto all electrodes at once by using a suction-holding device or a mask. When a suction-holding device is used, solder balls are held by suction in a suction-holding jig having suction-holding holes at the same positions as those of electrodes on the BGA substrate. Then, the solder balls are released directly above the respective electrodes, thereby mounting the solder balls onto the electrodes. When a mask is used, one that has holes at the same positions as those of the electrodes is placed over the BGA substrate. Then, solder balls are rolled on the mask and inserted into the respective holes of the mask, thereby allowing the solder balls to be mounted onto the electrodes. In other words, when solder balls are mounted on the BOA substrate by holding the balls with the suction-holding jig or by inserting them into the holes of the mask, the solder balls can be mounted onto the electrodes without any problems, no matter which portion of a solder ball is held by suction in a hole of the jig or inserted into a hole of the mask, because the solder balls have no directional property.
Columns mounted on a CGA are of circular cylindrical shape. Therefore, the columns cannot be held easily with a suction-holding jig as in the case of solder balls. Moreover, if a CGA fails to be loaded with all of a large number of columns required, it cannot function as an electronic component. That is, the lack of even only one column results in a defective CGA.
The present inventors disclose a column alignment device having an alignment plate provided with the same number of elongate grooves as the number of electrodes at one side of a ceramic substrate of a CGA. Each groove has the same width as the electrode width. A cover member is placed on the alignment plate to remove columns anywhere other than the grooves. The alignment plate is installed on a rectilinear feeder. A column supply device is installed in the neighborhood of the alignment plate to supply columns onto the alignment plate. [see Japanese Patent Application Unexamined Publication (KOKAI) No. 2004-200280].
Further, the present inventors disclose a column suction-holding head provided with the same number of grooves as the number of electrodes in one row on a ceramic substrate of a ceramic column grid array. The grooves are arranged at the same pitch as the column mounting pitch on the ceramic substrate. Suction holes are bored in the grooves and connected to a vacuum device. [see Japanese Patent Application Unexamined Publication (KOKAI) No. 2004-221287]. The present inventors also disclose a column mounting jig having a heat-resisting plate provided with holes at the same positions as those of electrodes on a ceramic substrate of a CGA. The plate is formed with positioning portions that allow the hole positions to coincide with the corresponding electrodes of the ceramic substrate when the plate is placed over the ceramic substrate. The plate is further formed with spacer portions that allow a predetermined gap to be provided between the reverse side of the plate and the ceramic substrate. [see Japanese Patent Application Unexamined Publication (KOKAI) No. 2004-228125].